A joke is not a thing but a process, a trick you play on the listener's mind. You start him off toward a plausible goal, and then by a sudden twist you land him nowhere at all or just where he didn't expect to go. ↗
We are concerned that, in a few years time, this place of discovery, with its wealth of human fossils, the like of which can be found nowhere else in the world, could be completely destroyed. ↗